1. Field of the Invention
This invention relates to free-space optical communication systems, and in particular, to improved mechanical features that enable alignment of the optical transceiver nodes.
2. Description of the Related Art
Over the last several years there has been tremendous growth in the deployment of fiber-optic facilities by telecommunications carriers such as Regional Bell Operating Companies (RBOCs), cable carriers, and Competitive Local Exchange Carriers (CLECs). Deployment of these facilities along with the introduction of technologies such as OC-192 and DWDM has dramatically lowered the marginal cost of bandwidth on the fiber.
Thus, as a result of this development, there is extensive bandwidth and communications capability in carriers' backbone networks. However, many homes and offices do not have a practical solution to interface to these backbone networks. Consequently, direct attachment of potential customers to these backbone networks remains very expensive.
Currently, there are two practical methods for directly attaching customers to backbone networks such as optical fiber networks. These are buried or aerial fiber interconnections and microwave connections. However, both of these methods incur significant up-front costs before any revenue can be realized. In the case of buried or aerial fiber, these costs are associated with obtaining rights-of-way for the cable runs, and installing the cable by burying or hanging. In the case of a microwave system, these up front costs come not only from the cost associated with the microwave repeater equipment, but also from the costs associated with obtaining rights to the suitable portion of the spectrum. Therefore, system developers and integrators have sought long and hard to find suitable solutions to this “last mile” problem.
Free-space optical communication systems provide a solution to this “last mile” problem. Free-space systems may be designed to use one or more optical beams, usually generated by lasers, to carry and transmit data over the free space between two communication terminals or nodes. The transmitting communication node includes one or more lasers to generate an information-bearing optical beam. The corresponding receiving terminal or node, which has an optical detector and associated signal processing circuit, converts the information into an electrical signal for further routing or processing. A communication node may include at least one laser and one detector to operate as an optical transceiver.
It is desirable to facilitate the initial alignment of the transmitting node and the receiving node. Additionally, after initial installation has been completed, it may become necessary to quickly replace a damaged or dysfunctional node with a replacement node. It is further desirable to facilitate reestablishing the communication link by enabling the replacement node to be pre-aligned so that it can simply be directed to point to the same location as the transceiver in the node that has been replaced.